Molecular sieves such as the microporous crystalline zeolite and non-zeolitic catalysts, particularly silicoaluminophosphates (SAPO), are known to promote the conversion of oxygenates to hydrocarbon mixtures. Numerous patents describe this process for various types of these catalysts: U.S. Pat. Nos. 3,928,483; 4,025,575 and 4,252,479 (Chang et al.); 4,496,786 (Santilli et al.); 4,547,616 (Avidan et al.); 4,677,243 Kaiser); 4,843,183 (Inui); 4,499,314 (Seddon et al.); 4,447,669 (Harmon et al.); 5,095,163 (Barger); 5,191,141 (Barger); 5,126,308 (Barger); 4,973,792 (Lewis); and 15 4,861,938 (Lewis).
The process may be generally conducted in the presence of one or more diluents which may be present in the oxygenate feed in an amount between about 1 and about 99 molar percent, based on the total number of moles of all feed and diluent components fed to the reaction zone (or catalyst). Diluents include, but are not limited to, helium, argon, nitrogen, carbon monoxide, carbon dioxide, hydrogen, water, paraffins, hydrocarbons (such as methane and the like), aromatic compounds, or mixtures thereof. U.S. Pat. Nos. 4,861,938 and 4,677,242 particularly emphasize the use of a diluent combined with the feed to the reaction zone to maintain sufficient catalyst selectivity toward the production of light olefin products, particularly ethylene. The above U.S. patents are hereby incorporated by reference.
U.S. Pat. No. 4,499,327 (Kaiser) discloses a process for the production of light olefins from a feedstream comprising methanol, ethanol, dimethylether, diethylether, or mixtures thereof, comprising contacting the feedstream with a silicoaluminophosphate molecular sieve at effective process conditions to produce light olefins.
U.S. Pat. No. 4,849,091 discloses a two-stage regeneration arrangement for use in a fluidized catalytic cracking system providing initial coke combustion below catalyst in a low catalyst density, high efficiency contact zone followed by substantial separation of catalyst and regeneration gas and complete regeneration of catalyst particles in a dense bed regeneration zone. Catalyst and gas flow co-currently prior to this separation but flow counter-currently after the separation.
World Patent Application WO 99/01219 discloses a method for selectively converting oxygenates to light olefins in which desirable carbonaceous deposits are maintained on the total reaction volume of catalyst by regenerating only a portion of the total reaction volume of catalyst and mixing the regenerated portion with the unregenerated total reaction volume of catalyst. The method incorporates a fluidized bed reactor with continuous regeneration. In a preferred arrangement, the oxygenate feed is mixed with regenerated catalyst and coked catalyst at the bottom of a riser and the mixture is lifted to a disengaging zone. In the disengaging zone, coked catalyst is separated from the gaseous materials by means of gravity or cyclone separators. A portion of the coked catalyst to be regenerated is sent to a stripping zone to recover adsorbed hydrocarbons. Stripped spent catalyst is passed to a regenerator.
U.S. Pat. No. 4,547,616 discloses an improvement in a process for the conversion of oxygenate or alcohols to olefins by the operation of a fluidized bed in a turbulent fluidization regime at elevated temperatures and controlled catalyst activity. It is disclosed that the fluidized catalyst bed is maintained in a vertical reactor column having a turbulent reaction zone to achieve good mixing at a velocity greater than the dense bed transition velocity to a turbulent regime and less than transport velocity for the average catalyst particle. The superficial fluid velocity is disclosed in a range between about 0.3 to 2 meters per second. Provision is made for passing partially regenerated catalyst to the reactor fluidized bed of catalyst beneath the upper interface and sufficiently below to achieve good mixing in the fluid bed. It is further disclosed that the bed of catalyst in the reactor can be least 5 to 20 meters in height, preferably about 9 meters.
U.S. Pat. No. 4,328,384 discloses a process for the conversion of alcohols and related oxygenates in a riser reactor and a dense fluid catalyst bed wherein the catalyst is circulated through a plurality of satellite stripping-cooling zones for temperature control. The process comprises passing a suspension of vaporized reacted material and fluid catalyst particles comprising a zeolite material upwardly through a relatively disbursed catalyst riser followed by passing the suspension comprising products of reaction upwardly through a relatively dense fluid mass of catalyst particles with an extended residence time in order to achieve total conversion of the oxygenate. Catalyst is withdrawn from a lower portion of the relatively dense bed of catalyst particles and passed downwardly through a plurality of separate catalyst stripping-cooling zones prior to being returned to the riser reactor. Stripped products are removed from the stripping- cooling zones wherein products are separated above a more dense fluid mass of catalyst than in the separate catalyst stripping-cooling zones.
U.S. Pat. No. 4,873,390 (Lewis et al.) discloses a process for catalytically converting a feedstream, e.g., an aliphatic hetero compound, such as methanol, into a product, e.g., light olefins, wherein the conversion to olefins can be selectively enhanced as compared to the conversion to paraffins by employing a catalyst that is not completely regenerated, i.e., contains a desired quantity of carbonaceous material.
U.S. Pat. No. 4,929,780 (Wright et al.) discloses an integrated process of converting methanol and other lower molecular weights oxygenates to gasoline, distillate range liquid hydrocarbons, and ethylene. The patent discloses the use of a fixed bed reactor in conjunction with a fluidized bed reactor in order to increase the yield to ethylene.
In view of the sensitivity of many of the above-described hydrocarbon conversion processes to reaction variables such as temperature, catalytic activity, and space velocity, improved processes are sought for controlling the process in order to obtain desired conversion products while inhibiting the conversion to by-products. More specifically, improved fluidized bed hydrocarbon conversion processes are sought which require lower catalyst inventories, simplify operation, and provide a sufficient amount of active catalyst sites in order to enhance the conversion to the desired products without enhancing the conversion to by-products.